1. Field of the Invention
The present invention relates to vehicle position estimating apparatuses and vehicle position estimating methods, and, more particularly, to a vehicle position estimating apparatus and a vehicle position estimating method capable of estimating a vehicle position on the basis of a position (GPS position) calculated from a GPS signal received from a GPS satellite.
2. Description of the Related Art
Navigation apparatuses read out map data corresponding to a current vehicle position from a recording medium such as a CD-ROM, a DVD, or an HDD, and draw a map on a display screen on the basis of the read out map data, and in addition, display a vehicle mark at a fixed position on the display screen, and scroll the map in accordance with vehicle movement. In addition, navigation apparatuses have a route guidance function in which a route from a starting point to a destination is searched for and the obtained route is displayed on a map, and a POI display function in which a predetermined POI mark (landmark) is displayed on a map.
A position measuring device for measuring a vehicle position is a necessity for such navigation apparatuses. In a first known position measuring method, a vehicle position is autonomously estimated using an angle sensor such as a gyro sensor for detecting a vehicle travel direction and a distance sensor (vehicle velocity sensor) for detecting a distance traveled every predetermined point in time, and map matching is performed as appropriate so as to correct the vehicle position so that the vehicle position can be located on a road on a map. In a second known position measuring method, a vehicle position is estimated using both a position (GPS position) calculated from radio waves received from a GPS (Global Positioning System) satellite and a position acquired by a self-contained navigation sensor. As examples of this method, there are first and second known techniques described in Japanese Unexamined Patent Application Publication Nos. 2002-333332 and 2004-271293.
In the first known technique of the above-described second known position measuring method, if the prediction error of self-contained positioning data does not exceed a predetermined threshold value, a current vehicle position is calculated by combining GPS positioning data with the self-contained positioning data, and in contrast, if the prediction error of the self-contained positioning data exceeds a predetermined threshold value, a current vehicle position is calculated without combining the GPS positioning data with the self-contained positioning data.
In the second known technique of the above-described second known position measuring method, a vehicle position and a vehicle position range are predicted using a self-contained navigation sensor, and if a GPS-measured position exists within the predicted vehicle position range, the GPS-measured position is defined as a current vehicle position, and in contrast, if the GPS-measured position exists out of the predicted vehicle position range, the predicted vehicle position is defined as a current vehicle position.
In the first known technique, a current vehicle position is usually acquired by combining the GPS positioning data and the self-contained positioning data. That is, a GPS-measured position is not normally defined as a current vehicle position. In addition, even if the GPS-positioning data becomes unreliable, the self-contained positioning data is not used instead of the GPS positioning data.
In the second known technique, a GPS-measured position is acquired using GPS positioning data and map data. That is, the GPS-measured position acquired only from the GPS positioning data is not defined as a current vehicle position. In addition, a vehicle position and a vehicle position range are predicted using a self-contained navigation sensor all the time, and if a GPS-measured position exists within the predicted vehicle position range, the GPS-measured position is defined as a current vehicle position, and in contrast, if the GPS-measured position exists out of the predicted vehicle position range, the predicted vehicle position is defined as a current vehicle position.